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Background: Episodic collapse in horses has equine welfare and human safety implications. There are, however, no published case series describing this syndrome., Objectives: To characterize the cause and outcomes for horses referred for investigation of episodic collapse., Animals: Twenty-five horses referred for investigation of single or multiple episodes of collapse., Methods: Retrospective study. Clinical records from the Dick Vet Equine Hospital, University of Edinburgh from November 1995 to July 2009 were searched using the following keywords: collapse, collapsing, fall, syncope. Collapse was defined as an incident in which the horse lost postural tone with or without progression to recumbency and with or without loss of consciousness. Long-term follow-up information was obtained by telephone conversation with the owner., Results: A final diagnosis was reached in 11 cases, namely cardiac arrhythmia (4), right-sided heart failure (1), hypoglycemia (2), generalized seizures (2), and sleep disorder (2). A presumptive diagnosis was reached in 8 cases, namely neurocardiogenic syncope (5), exercise-induced pulmonary hemorrhage (2), and generalized seizures (1). No diagnosis was reached in 6 cases despite comprehensive investigations. Three horses were euthanized at presentation. Treatment was attempted in 9 horses with 6 cases having successful outcome before discharge. Follow-up information was available for 14 of 19 horses discharged from the hospital. Only 1 of these horses was observed to collapse after discharge., Conclusions and Clinical Importance: Definitive diagnosis was more likely to be reached in cases with multiple episodes of collapse. Horses in which 1 episode of collapse occurred did not necessarily collapse again., (Copyright © 2010 by the American College of Veterinary Internal Medicine.)

Lateral thoracic nerve reflex latencies values were measured in ponies using a simple, non-invasive technique. The reflex was elicited using an external triggering hammer attached to an electrodiagnostic unit. The resulting evoked, compound muscle action potentials were recorded with electrodes, which were placed over the 6th ribs or 11th rib level with the axilla. Two superimposed repeats of 4 signal-averaged sweeps of 50 or 100 milliseconds were recorded and the estimated reflex pathway was measured for each subject in order to calculate the reflex latencies and latency velocities. Mean left and right 6th rib peak latencies were not significantly different from each other (P = .609), but left 6th rib latencies were shorter than those recorded from the 11th rib (P < .0001), substantiating the existence of an indirect (central) pathway to the reflex. The calculated left and right 6th rib latency velocities were not significantly different from each other (P = .58) but left 6th rib latency velocities were different from left 11th rib (P = .009). The calculated latency velocities were within the broad range for corticospinal tract motor conduction velocities and comparable to magnetic motor evoked latency velocities. The use of lateral thoracic reflex latency measurements to objectively identify the site of spinal cord lesions is discussed.

Magnetic stimulation of motor pathways was used to effect motor unit action potential recordings from forelimb and hindlimb muscles in unanesthetized ponies. Motor pathway conduction velocities to the forelimb and hindlimb were determined to be 53.8 +/- 9.6 m/s-1 and 63.4 +/- 8.3 m/s-1, respectively. This noninvasive technique will enable more precise evaluation of motor deficits in clinical patients than is possible with the neurological examination.

Parameters for the accuracy of clinical diagnosis of neurologic diseases in the horse were determined from 210 horses in which a definitive pathologic diagnosis was confirmed. The overall efficiency of diagnosis for all diseases was 0.95 although the validity varied from 0.79 to 1.00, the sensitivity varied from 0.73 to 0.95, and the specificity varied from 0.88 to 1.00 for individual disease categories. Equine protozoal myeloencephalitis was overdiagnosed, whereas Eastern equine encephalomyelitis, equine degenerative myeloencephalopathy, and traumatic neurologic disease were underdiagnosed. The use of such measurements of accuracy of diagnosis parameters in clinical practice will allow new diagnostic techniques to be objectively evaluated, resulting in greater efficiency of diagnosis and therapy.

Following a workshop on equine protozoal myeloencephalitis (EPM) convened at the Veterinary Medical Forum of the American College of Veterinary Internal Medicine in 1988, this survey of EPM in North America was developed. It is based upon 364 histologically confirmed case records from California, Florida, Illinois, Kentucky, New York, Ohio, Oklahoma, Ontario, Pennsylvania, and Texas up to 1988. The highest rate of infection was found in young Thoroughbred, Standardbred, and quarter horses. Differences in geographic location, sex, and month (season) of infection were not discernible. This report, the first comprehensive survey of EPM in North America, is intended to serve as a basis for evaluating future changes in prevalence and spread of EPM.

A group of 834 Thoroughbred horses was surveyed on four central Florida farms for clinical and epidemiologic features of anhidrosis. In addition, comparative analysis was made of serum thyroxine, serum electrolytes, and fractional urinary electrolyte excretion ratios. An overall disease prevalence of 6.12% was observed. Training horses and nonpregnant broodmares had a predilection for the disease. Adolescent horses were infrequently affected. There was no correlation with sex or color. Comparative clinical signs, related to thermoregulatory compromise, included tachypnea and hyperthermia. Long-term effect included focal and generalized alopecia, decreased appetite, and impaired performance. Previously reported hypothyroidism and hypochloremia were not demonstrated; however, fractional urinary chloride excretion ratios indicated a significant relative conservation of chloride.

Two horse farms, on which there was a high incidence of proven and suspected equine degenerative myeloencephalopathy (EDM), were studied. Symmetric ataxia and paresis, along with laryngeal adductor, cervicofacial, local cervical, and cutaneous trunci hyporeflexia, characterized the syndrome. Serum vitamin E concentration reflected a deficient state in affected and unaffected horses on both farms when compared with selected reference groups and with published values. A high incidence of the disease was evident in offspring of two particular sires on one farm. Vitamin E supplementation resulted in correction of the deficient state in most horses and was associated with a drastic reduction in the incidence of EDM on one farm from 40% to less than 10% the year following vitamin E supplementation. In addition, during the last year, the severity of signs in the few cases was dramatically reduced. This information substantiates the hypothesis that EDM is a vitamin E-responsive disorder of Equidae with a possible familial predisposition.